Hydrocarbon isomerization catalysts and procedures for the preparation and use thereof

ABSTRACT

Hydrocarbon isomerization catalysts comprising typically refractory mineral oxide carrier such as alumina and a halogen element present in combined form, together with, in the free or combined state: A platinum-group metal; second element from the group consisting of titanium, zirconium, tungsten and molybdenum; and a metal halide such as AlCl3.

This is a division of application Ser. No. 936,686, filed Nov. 7, 1978,now U.S. Pat. No. 4,201,696, which is a continuation of application Ser.No. 713,238, filed Aug. 10, 1976, and now abandoned.

The present invention relates to new catalysts for the isomerization ofhydrocarbons, and particularly of normal paraffins, a process for thepreparation of said catalysts, and the application thereof to theisomerization of hydrocarbons.

Many isomerization catalysts of varying compositions have already beenproposed. These catalysts generally are formed by a carrier, which maybe an alumina, an aluminosilicate, or a mixture of the two. Among theknown isomerization catalysts there are those comprising a noble metal,and particularly platinum, with which may be associated tin, nickel,germanium, rhenium, lead and certain metals of groups Ib, IIb, Vb, VIIb,III and IV of the periodic table of the elements, and comprising furthera metal halide such as aluminum trichloride.

The applicants have developed new catalysts having satisfactorycatalytic properties in their application to the isomerization ofhydrocarbons.

The present invention thus has as its object to provide new catalystsfor the isomerization of hydrocarbons which have good activity and goodselectivity.

The invention consequently has as a first embodiment, catalysts for theisomerization of hydrocarbons comprising a carrier formed at least inpart by at least one refractory mineral oxide, and comprising a halogenelement present in combined form, said catalysts being characterized bythe fact that they comprise and/or consist essentially of, in the freeor combined state:

At least one platinum-group metal, and preferably platinum;

at least one second element selected from the group consisting oftitanium, zirconium, molybdenum and tungsten; and

at least one metal halide.

In this definition of the invention, and throughout the presentapplication, "platinum-group metal" means one of the following metals:Ruthenium, rhodium, palladium, osmium, iridium and platinum.

A second embodiment of the present invention is a process for thepreparation of catalysts in accordance with the invention, said processbeing characterized by the fact that it involves the following steps:

At least one impregnation with at least one solution containing at leastone element selected from the group consisting of titanium, zirconium,molybdenum, tungsten and the platinum-group metals, and

an aftertreatment with a metal halide employing means known in the art.

A third embodiment of the present invention is a process for theisomerization of hydrocarbons characterized by the fact that saidhydrocarbons are contacted, under conditions known in the art, withhydrogen and at least one of the catalysts in accordance with theinvention.

The carriers of the catalysts in accordance with the invention should berefractory materials having sufficient specific surface and specificpore volume and having, moreover, acid sites. The specific surface maybe comprised between 15 and 350 m² per gram, and preferably between 100and 350 m² per gram, the specific pore volume being greater than 0.1 cm³per gram. These materials (often referred to as a refractory mineraloxide, or more commonly as a refractory metal oxide) may, for example,be alumina, silica, an aluminosilicate, magnesia, zirconia, the oxidesof gallium, titanium, thorium or boron, or a mixture of these oxides.

The most advantageous catalysts are those whose platinum-group metalcontent is comprised between 0.02 and 2%, based on the weight of thecarrier. To obtain satisfactory catalytic properties, said content ispreferably held above 0.10%; however, for reasons of catalyst cost, itis preferably limited to 0.75%. The weight percentage given herein arereferred to the elemental form.

The content of metal or metals selected from the group consisting oftitanium, zirconium, molybdenum and tungsten is comprised between 0.005and 8%, based on the weight of the carrier, since below 0.005% noimprovement is observed over a catalyst containing only platinum, andabove 8% the increase in content does not entail a significant increasein activity. Moreover, the applicants have found that the mostefficacious contents are those comprised between 0.01 and 3%.

The total halogen content may be comprised between 0.1 and 15%, andpreferably between 0.5 and 7%, based on the total catalyst weight.

The process for preparation of the catalysts in accordance with theinvention involves a first step consisting of the deposition of themetals on the carrier by known means, for example, by impregnation withsolutions containing said metals, either as anions or cations. They maybe deposited in any order and the titanium, zirconium, molybdenum,tungsten and platinum-group metals may be deposited simultaneously orsuccessively. However, the applicants have found that it is preferableto deposit the platinum-group metal or metals last with the lastimpregnating solution.

The acidity of the carrier may be altered in the course of the variousimpregnations, particularly by means of a treatment with an acidsolution, for example, a solution of hydrochloric acid. The activity ofthe acid sites present on the carrier may thus be increased.

After the deposition of the metals, the carrier may be dried, thencalcined at a temperature which in the case of the metals other than theplatinum-group metals is comprised between 400° and 700° C., andpreferably between 500° and 650° C., and in the case of theplatinum-group metals is under 600° C. In the case of platinum, it ispreferably less than 550° C.

At the conclusion of the deposition of the metals on the carrier, thehalogen content of the solid obtained is comprised between 0.1 and 2%,based on the weight of the carrier. The halogen, preferably chlorine, iscombined with the elements forming the carrier and/or with the elementsdeposited on the carrier at the end of the impregnation treatment. Inthe remainder of this specification, it will be referred to as the"combined halogen."

The deposition of the metals on the carrier is followed by a treatmentwith a metal halide from the group consisting of aluminum trichloride,aluminum tribromide, ferric chloride or bromide, beryllium or zirconiumchloride, or any mixture of these halides. However, the applicantsprefer to use aluminum trichloride.

Before the treatment with the metal halide is carried out, it is,however, preferable to adjust the "combined halogen" content of thesolid to be treated. This adjustment of the "combined halogen" contentmay be effected, for example, by treating said solid with a gaseousmixture of steam and halogen compound, which may be diluted in anothergas or mixture of gases such as air, particularly at a temperaturecomprised between 400° and 700° C. and on the order of 500° C., forexample. If the halogen is chlorine, a steam-hydrogen chloride mixture,for example, may be used. After this gas treatment, the solid may bedried at between 80° and 320° C., then calcined at between 370° and 600°C. for a time which may vary but should be less than 10 hr. and shouldpreferably be comprised between 1 and 5 hr.

It is then necessary to treat the solid with an anhydrous gas, that isto say, a gas containing less than 20 ppm of water by volume, justbefore the metal halide is deposited. Good results are obtained bypassing a stream of hydrogen substantially free from water over thesolid at a temperature comprised between 400° and 700° C., andpreferably between 400° and 600° C., for a time of about 1 to 10 hr.

Before the metal halide treatment, the solid so obtained containsslightly more "combined halogen" than after the deposition of the metalson the carrier. For example, if the solid initially contained from 0.1to 2% by weight of the composition of "combined halogen", the solidobtained may contain from about 0.8 to 2.5% of "combined halogen" afterthe halogen-content adjusting step.

The metal halide treatment may be effected by any suitable means knownin the art. For example, aluminum trichloride may be sublimed on theproduct at a temperature comprised between about 190° and 700° C., andpreferably between 200° and 600° C., under atmospheric or higherpressure, in the presence of diluent gases such as hydrogen, inertgases, or light paraffinic hydrocarbons. The impregnation may beeffected discontinuously but it is preferable to proceed by passingsublimed aluminum trichloride vapors in admixture with a gas such ashydrogen over the catalyst. The halide then becomes fixed on the solidpreviously obtained. However, to eliminate the unreacted halide, thecatalyst must be brought to a temperature above 300° C. and scavengedwith an inert gas such as nitrogen. The duration and temperature of thislatter treatment depend on the excess of unfixed metal halide thatremains on the catalyst. Generally, a temperature of from 400° to 700°C. and preferably comprised between 500° and 600° C., and a duration offrom 1 to 48 hr. will suffice to eliminate this excess. The catalystultimately obtained in this last step contains from 0.1 to 15%, andpreferably from 0.5 to 7%, of total halogen, based on the total weightof the catalyst, the preferred halogen being chlorine. "Total halogen"means both the "combined halogen" defined earlier and the halogenresulting from the metal halide treatment.

The catalysts in accordance with the invention are intended to be usedin a process for the izomerization of hydrocarbons, and moreparticularly of paraffinic hydrocarbons. The conditions of temperatureand pressure are known in the art. Thus, the temperature is comprisedbetween 20° and 450° C., the pressure between 1 and 100 atmospheres(hydrogen pressure), the molar ratio of hydrogen to hydrocarbons(introduced into the reactor) ranging from 0.5 to 20, and the spacevelocity, measured in the liquid state and based on the volume of chargepassing over a unit volume of catalyst in one hour (vol./vol./hr.),being comprised between 0.1 and 10. A wide range of hydrocarbon chargesmay be treated. Besides xylenes, olefins and other charges, theapplicants have found that the catalysts in accordance with theinvention are very well suited to the isomerization of paraffinichydrocarbons.

In fact, the catalysts ultimately obtained have proved more advantageousthan a conventional catalyst containing only platinum and a metal halidedeposited on a refractory mineral oxide carrier, as will be shown by theexample which follows, which is in no wise limitative and is given onlyby way of illustration.

In this example, the charge consists of normal pentane, the hydrocarbongenerally used to test isomerization catalysts; but it might alsoconsist of the hydrocarbons mentioned earlier.

EXAMPLE 1

This example relates to the preparation and utilization of six catalystsin accordance with the invention. There will be described successivelythe preparation of six catalysts A1, A2, B1, B2, C and D as well as thatof two control catalysts T1 and T2, then their application to thehydro-isomerization of normal pentane.

Preparation of Catalysts

The refractory carrier used with all of the catalysts described below isan alumina whose characteristics are as follows:

    ______________________________________                                        Specific surface:   190 m.sup.2 /g                                            Pore volume:        0.51 cm.sup.3 /g                                          Average pore radius:                                                                              53 A                                                      Chlorine content                                                              (measured by x-ray  0.4% by weight                                            fluorescence):      of the alumina                                                                Extrudator with an                                        Form:               average diameter                                                              of 1.5 mm                                                 ______________________________________                                    

This alumina, calcined for 4 hr. at 600° C. before the deposition of thevarious metals, will hereinafter be called the "carrier alumina."

Preparation of Control Catalysts T1 and T2

The carrier alumina is immersed in a dilute hydrochloric acid solutionof a normality of about 0.1 N. After dewatering at ambient temperature,the alumina is contacted with a circulating solution ofhexachloroplatinic acid whose initial platinum concentration is suchthat the catalyst contains about 0.35% by weight of platinum. Afterdewatering followed by drying at 120° C., the solid is calcined at about530° C. in a muffle kiln.

The solid is then subjected to a treatment for adjustment of itschlorine content. To this end, a gaseous stream of steam and hydrogenchloride is passed over it at a temperature of 500° C. for 4 hr. Thesolid obtained is then calcined for 1 hr. at the same temperature.

Finally, the solid is subjected to a reduction with hydrogen for about 1hr. at 500° C. It contains 1.36% chlorine and 0.33% platinum.

In order to obtain the two control catalysts, the solid is then dividedinto two portions, which are then separately subjected to the aluminumchloride treatment.

13 grams of each portion is scavenged with a stream of sublimed aluminumtrichloride and hydrogen (total pressure of gas stream, 1 atmosphere;partial pressure of aluminum trichloride, 30 torr).

For the first portion, which will form the catalyst T1, this treatmentis effected for 21/2 hr. at 300° C.

For the second portion, which will form the catalyst T2, this treatmentis effected for 21/2 hr. at 500° C.

The two portions are then treated with a stream of anhydrous nitrogen atabout 500° C. for elimination of the unreacted aluminum trichloride.

Thus the two controls T1 and T2 are obtained. Their characteristics arepresented in Table 2.

Preparation of Catalysts A1, A2, B1, B2, C and D

100 g of carrier alumina is impregnated with 250 cm³ of a solutioncontaining 20 cm³ of hydrochloric acid RP and a certain weight of acompound of titanium, molybdenum, zirzonium or tungsten, depending onthe catalyst to be prepared. The weights and compounds are given inTable 1 below.

                  TABLE 1                                                         ______________________________________                                                                 Weight of Compound                                   Catalyst                                                                              Compound Used    (grams)                                              ______________________________________                                        A1      Ti.sub.2 (C.sub.2 O.sub.4).sub.3 . 10H.sub.2 O                                                 0.8962                                               A2      Ti.sub.2 (C.sub.2 O.sub.4).sub.3 . 10H.sub.2 O                                                 2.3315                                               B1      ZrO(NO.sub.3).sub.3 . 2H.sub.2 O                                                               0.327                                                B2      ZrO(NO.sub.3).sub.3 . 2H.sub.2 O                                                               0.980                                                C       (NH.sub.4).sub.6 Mo.sub.7 O.sub.24 . 4H.sub.2 0                                                0.184                                                D       (NH.sub.4).sub.10 W.sub.12 O.sub.41 . 7H.sub.2 O                                               0.4438                                               ______________________________________                                    

After evaporation in a rotary evaporator, the catalyst is dried at about120° C., then calcined for 2 hr. at 600° C.

There are then effected an acidification of the carrier, an impregnationwith a hexachloroplatinic acid solution, an adjustment of the chlorinecontent and a reduction with hydrogen which are identical in allrespects with the operations described earlier for control catalysts T1and T2.

The solids obtained are then subjected to an aluminum trichloridetreatment identical with the one effected on T1 for 21/2 hr. at 300° C.

The compositions of the catalysts T1, T2, A1, A2, B1, B2, C and D arepresented in Table 2 below.

                  TABLE 2                                                         ______________________________________                                        Composition in wt. % in solid                                                 before AlCl.sub.3 treatment                                                                           Per cent     Final chlorine                           Cata-          Other    of other     content of                               lyst   Pt      Metal    metal   Cl   catalyst, wt. %                          ______________________________________                                        T1     0.33                     1.36 5.85                                     T2     0.33                     1.36 4.68                                     A2     0.36    Ti       0.22    1.45 5.88                                     A2     0.35    Ti       0.60    1.22 5.48                                     B1     0.38    Zr       0.23    1.30 5.58                                     B2     0.38    Zr       0.46    1.16 5.19                                     C      0.36    Mo       0.14    1.35 5.38                                     D      0.36    W        0.26    1.23 5.81                                     ______________________________________                                    

Catalytic Tests

Catalytic tests are then performed on each of these catalysts in thefollowing manner: Normal pentane and hydrogen are passed, at a pressureof 30 bars and a temperature of 150° C., over 10 cm³ of catalyst placedin a reactor. The space velocity, defined earlier, is 3, and the molarratio of H₂ to hydrocarbon is 2.5.

The only reaction product is isopentane. The activity of the variouscatalysts may therefore be evaluated on the basis of the conversion ofthe normal pentane. The results are reported in Table 3 for eachcatalyst.

                  TABLE 3                                                         ______________________________________                                        Catalyst    Conversion of normal pentane, %                                   ______________________________________                                        T1          43                                                                T2          40                                                                A1          55                                                                A2          54                                                                B1          62                                                                B2          62                                                                C           60                                                                D           48                                                                ______________________________________                                    

From these results, it is apparent that the catalysts in accordance withthe invention possess good activity for isomerization. In fact, thecatalysts in accordance with the invention exhibit considerably greateractivity than the control catalysts containing only platinum.

EXAMPLE 2

With a view to verifying the good behavior with time (stability) of thecatalytic formulations in accordance with the invention, a catalytictest comparable to that described in Example 1 was run on the followingcatalyst:

Carrier: An alumina identical with that of Example 1:

    ______________________________________                                        Pt              0.35%                                                         Zr              0.33%                                                         Cl              3.81%                                                         ______________________________________                                    

The charge was normal pentane to which 100 ppm of chlorine in the formof 1-2-dichloropropane had been added. The volume of catalyst in thereactor here was 25 cm³, the space velocity was 5, and the molar ratioof hydrogen to normal pentane was 3.

The graph in the drawing shows the evolution of the ispentane yield ofthe reaction. The graph shows the percentage of isopentane formed in theisomerization reaction extended for more than 400 hours. This yield isdefined as the ratio of number of molecules of isopentane to number ofmolecules having five carbon atoms.

As may be seen, the catalyst is very stable with time. Moreover, ananalysis of the catalyst at the end of the test showed that it containedonly 0.13% carbon, which is very little.

We claim:
 1. A process for the isomerization of hydrocarbons comprisingcontacting said hydrocarbons under conditions favoring isomerizationwith hydrogen and a catalyst consisting essentially of a carrier whichis comprised of at least one refractory metal oxide, including a halogenelement present in combined form, and deposited on said carrier:fromabout 0.02 to 2 wt. %, based on the weight of the carrier, of at leastone platinum-group metal; from about 0.005 to 8 wt. %, based on theweight of the carrier, of at least one second element from the groupconsisting of titanium, zirconium, tungsten and molybdenum; and at leastone metal halide based on the weight of the carrier, selected from thegroup consisting of aluminum trichloride, aluminum tribromide, ferricchloride, ferric bromide, beryllium dichloride, zirconium chloride andmixtures thereof, the total halogen content of said catalyst being 0.1to 15 wt. % of the total weight of the catalyst, wherein at least one ofsaid platinum group metal and at least one second element are introducedonto the carrier by impregnation and thereafter at least one metalhalide is introduced onto the carrier by sublimation.
 2. In the processof claim 1, the further improvement wherein the process for thepreparation of said catalyst comprises the following steps:at least oneimpregnation of the carrier with at least one solution containing atleast one element from the group consisting of titanium, zirconium,molybdenum, tungsten and the platinum-group metals, at least one of theimpregnating solutions comprising either cations of the elementstitanium, zirconium, molybdenum and tungsten, or anions containing saidelements, and an aftertreatment with at least one metal halide selectedfrom the group consisting of aluminum trichloride, aluminum tribromide,ferric chloride, ferric bromide, beryllium dichloride and zirconiumchloride.
 3. A process for the isomerization of hydrocarbons comprisingcontacting said hydrocarbons under conditions favoring isomerizationwith hydrogen and a catalyst consisting essentially of a carrier whichis comprised of at least one refractory metal oxide, including chlorinepresent in combined form, and deposited on said carrier:from about 0.10to 0.75 wt. %, based on the weight of the carrier, of platinum; a secondelement of zirconium; a metal halide of aluminum trichloride, andwherein at least one of said platinum group metal and at least onesecond element are introduced onto the carrier by impregnation andthereafter at least one metal halide is introduced onto the carrier bysublimation wherein the percentages of said platinum, said secondelement, and said chlorine are respectively 0.10 to 0.75 wt. %, 0.01 to3 wt. % and 0.5 to 7 wt. %, and wherein said carrier is an aluminahaving a specific surface comprised between 100 and 350 m² /g, and aspecific pore volume greater than 0.1 cm³ /g, and said carrier has acidsites.
 4. A process for the isomerization of hydrocarbons comprisingcontacting said hydrocarbons under conditions favoring isomerizationwith hydrogen and a catalyst, the improvement wherein said catalystconsists essentially of a carrier comprised of at least one refractorymetal oxide, including a halogen element present in combined form in anamount from 0.1 to 2.5 wt. %, and the following deposited on saidcarrier:from 0.02 to 2 wt. % of platinum; from 0.005 to 8 wt. % ofzirconium; and said percentages being based on the elemental formrelative to the weight of the carrier; the total halogen content of saidcatalyst being 0.1 to 15 wt. % of the total weight of the catalyst; andsaid process comprises the following steps: at least one impregnation ofthe carrier with at least one solution containing at least one elementfrom the group consisting of titanium, zirconium, molybdenum, tungstenand the platinum-group metals, at least one of the impregnatingsolutions comprising either cations of the elements titanium, zirconium,molybdenum and tungsten, or anions containing said elements, and anaftertreatment with at least one metal halide selected from the groupconsisting of aluminum trichloride, aluminum tribromide, ferricchloride, ferric bromide, beryllium dichloride and zirconium chloride,and wherein at least one of said platinum group metal and at least onesecond element are introduced onto the carrier by impregnation andthereafter at least one metal halide is introduced onto the carrier bysublimation.
 5. A process according to one of claims 1 to 3 or 4,wherein the hydrocarbons subjected to isomerization are paraffinichydrocarbons.
 6. A process according to one of claims 1 to 3 or 4,wherein the isomerization conditions comprise a temperature of between200° and 450° C., a hydrogen pressure of between 1 and 100 atmospheres,a molar ratio of hydrogen to hydrocarbons of from 0.5 to 20, and a spacevelocity measured in the liquid state of between 0.1 and 10 volumes ofcharge per volume of catalyst per hour.
 7. A process according to claim6, wherein the hydrocarbons subjected to isomerization are paraffinichydrocarbons.
 8. A process according to claim 6, wherein thehydrocarbons subjected to isomerization comprise xylenes or olefins.